In conventional mass storage devices, a defect table of a fixed, predetermined size, length and/or capacity is stored on the recording medium of each storage device. The defect table indicates unreliable portions of the recording medium. During production of the mass storage device, the mass storage device is tested to determine which portions, if any, of the recording medium are not sufficiently reliable for writing and reading of data. The address of the each of the unreliable portions is stored on the recording medium in the defect table.
Furthermore, the size of the defect table on the recording medium in conventional mass storage device is predetermined, and fixed, regardless of how many actual defects are found during testing. When the number of defects is greater than the capacity of the defect table on the recording medium, the mass storage device is discarded as unusable because unreliable portions of the mass storage device will not be identified in the defect table on the recording medium.
During operation of conventional mass storage devices, the defect table on the recording medium is read and the entire defect table on the recording medium is cached in a defect table in memory on the microcontroller or microprocessor of the mass storage device. The defect table on the recording medium has a predetermined size because of the limited size of the defect table in memory. The cached defect table is referred to by the microcontroller or microprocessor to determine which portions of the recording medium not to use.
For example, when the microcontroller or microprocessor receives a write command, the microcontroller or microprocessor will determine that the addresses indicated in the cached defect table that will not be used for writing data. When the defect table on the recording medium is cached, the entire defect table on the recording medium of the fixed size is cached. However, when the entire defect table is cached, the limitation of the size of the cached defect table limits the size of the defect table on the recording medium. This has problems, in that when the number of defects on the recording medium is less than the capacity of the cached defect table, memory is unnecessarily reserved for the cached defect table. In addition, the cached defect table is not optimized or adapted to the application of the mass storage device or the quantity of defects on the recording medium.
Where the mass storage device is a disc drive, during operation of disc drive, for every disc access, the target address is expressed as logical block address (LBA). The LBA is converted to a physical address expressed as a physical cylinder/head/sector (PCHS) address based on the physical layout of the drive and the information in the defect table.
One conventional scheme of managing defect tables is the fixed-spares-per-track defect scheme (FSPT). In FSPT, each track is allocated a fixed amount of spares throughout the whole disc drive. Defective sectors are slipped using the spare sectors assigned to each track. Unused spares can be used to replace grown defects that may occur during the drive's lifetime. When a track has more defective sectors than the reserved spare sectors, some of the sectors are reassigned to another track using linear replacement method to achieve the same logical sectors per track. In LBA to physical block address (PBA) translation using FSPT, the translation is based on a logical zone table that describes the logical layout of the drive.
FIG. 1 is a block diagram of a table 100 of a physical zone layout according to the conventional FSPT scheme of managing defects. FIG. 2 is a block diagram of a table 200 of a logical zone layout according to the conventional FSPT scheme of managing defects.
The physical zone layout table 100 differs from the logical zone layout 200 in that one spare sector is reserved for every track. The conversion process from LBA to PCHS is accomplished by using the logical zone table 200 only as all logical zones are guaranteed a fixed number of sectors per zone.
FIG. 3 is a block diagram of a table 300 of track defects according to the conventional FSPT scheme of managing defects. During operation the entire defect table 300 is cached. The portions of the defect table 300 that correspond to, or are associated with, infrequently used or least recently used portions of the recording medium of mass storage device are cached. This is problematic in that infrequently used portions of the defect table 300 are cached. Therefore the cached defect table occupies more memory space than is typically useful.
The mass storage device is unusable when the defect table is larger than the defect buffer. During operation of the mass storage device, the cached version of the defect table (i.e. the defect buffer) will be updated when reliability problems are encountered with portions of the recording medium that are not identified by the defect table 300. The addresses of the grown defects of the recording medium will be added to the cached defect table. Later, the defect table 300 that stored on the recording medium will be updated with the cached defect table. However, if the quantity of defects stored in the defect table 300 on the recording medium is equal to the maximum capacity of the quantity of defects that can be cached, the mass storage device is rendered unusable.
Furthermore, seek times can be lengthy when a singular defect table is physically distant from some of the data on the recording medium. The singular defect table on the recording medium is stored in a reserved portion of the recording medium. During operation of the mass storage device, the seek time between accesses to the defect table and the regions of the recording medium that store data can be relatively lengthy because of the relatively large physical distance between the defect table in the reserved area and the data regions.
What is needed is a system, method and apparatus that enables a defect table on the storage medium that is adaptable and dynamic in size, capacity and length to accommodate the actual number of defects on the recording medium. What is also needed is a system, method and apparatus that enables a cached defect table that is adaptable and dynamic in size, capacity and/or length to the portions of the defect table that correspond to, or are associated with, frequently used or most recently used portions of the recording medium of mass storage device. What is also needed is a system, method and apparatus that provides a defect table on the recording medium of the storage device that has a larger capacity than the defect buffer. What is also needed is a system, method and apparatus that provides the defect table on the recording medium to be stored in a manner that reduces the seek time between the regions of data and the defect table. What is further needed is a system, method and apparatus that provides a defect table on the volatile memory device of the mass storage device that is adapted or optimized in reference to the application of the mass storage device and/or the quantity of defects on the recording medium.